Phase-Precession-Like Effects in the Anterior Insula Cortex during Reward Expectancy

Reward expectancy contributes to cognitive performance and is governed by the anterior insular cortex (AIC). To investigate the electrophysiological mechanisms underlying reward expectancy in the AIC, we collected intracranial electroencephalography (iEEG) data from epilepsy patients implanted for clinical purposes while they were navigating a virtual T-maze. During navigation, subjects encountered rewards at three pre-defined locations. We focused on the time window proximity to entering the reward zone, which was defined as the reward-expectancy stage. A strong phase-amplitude coupling (PAC) between local theta phase and gamma power within the AIC has been reported at the expectancy stage of rewards. Interestingly, the PAC effect exhibited a specific temporal structure in which the gamma power was progressively coupled to earlier theta phase before each onset of the same reward. Meanwhile, the reward-specific brain patterns were pre-activated during the expectancy stage of rewards, taking place slightly prior to the occurrence of peak gamma activities across individual trials. Furthermore, the pre-activation of reward-specific patterns also progressively shifted forward on theta phases as more trials were conducted. These phenomena of phase shift were reminiscent of the phase precession effect in which single neurons fire at progressively earlier phases of low-frequency oscillations, and thus were called phase-precession-like effects (PPLEs). Additionally, subjects exhibiting PPLEs in the AIC presented less variability and a more notable improvement in response latency across trials. These results indicate that PPLEs in the AIC play an important role in reward expectancy which in turn facilitate task performance. ![Figure][1] ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes